1. Field of the Invention
The present invention relates to a fixing apparatus that is to be mounted in an electrophotographic image forming apparatus such as a copying machine or a printer.
2. Description of the Related Art
As a fixing apparatus of an image forming apparatus such as a copying machine or a laser printer, PTL 1 discloses a fixing apparatus employing a method of making a toner image on a recording material fix onto the recording material by supplying electricity to a heat generating layer provided on a belt and causing the belt itself to generate heat. A fixing apparatus employing such a method reaches a state of being able to perform fixing in a short time after the fixing apparatus is powered on and has an advantage of speeding up of start-up.
A problem of a fixing apparatus employing a belt which has a heat generating layer will be described with reference to FIG. 12A and FIG. 12B. In FIG. 12A, electrodes 5a and 5b for energizing are in contact with ends of a belt 1 in the direction perpendicular to the direction of rotation of the belt 1, and the belt 1 is energized by an AC power supply V via the electrodes 5a and 5b so as to generate heat. In this case, the current density of the flowing current reaches the highest value in an area of a straight line connecting the electrodes 5a and 5b, and the amount of heat generation also reaches the highest value in the same area. Because of this, the amount of heat generation becomes high in the area of the straight line connecting the electrodes 5a and 5b and becomes low in areas far from the area of the straight line connecting the electrodes 5a and 5b, and as a result, heat is unevenly generated in the direction of rotation of the belt 1.
To eliminate the unevenness in heat generation in the direction of rotation of the belt 1, for example, as shown in FIG. 12B, electrically conductive layers 4a and 4b are provided at the ends of the belt 1 to make the current flow throughout the belt 1. PTL 1 discloses a configuration in which electrically conductive layers are provided at ends of an outermost layer of a belt and extend along the outermost layer in the direction of rotation of the belt, and in which power supplying rollers or electrode brushes are placed so as to be in contact with the electrically conductive layers to supply electricity to the electrically conductive layers. Having such a configuration enables the current to uniformly flow throughout the belt 1, and as a result, the unevenness in heat generation in the direction of rotation of the belt 1 can be eliminated.
However, since the electrically conductive layer is formed by applying or bonding a conductive ink, a conductive paste, a metallic foil, a metallic mesh or the like to the belt, if the electrically conductive layer slides while being in contact with an electrode portion, the electrically conductive layer may sometimes be scraped with long-term use. This results in unevenness in heat generation, and thus there is a problem that unevenness in heat generation cannot be suppressed for long periods of time.